1. Field of the Invention
Microporous hollow fibers have many uses, for example for fluid and gas separation. Bundles of hollow fibers, which share a common header for incoming feed material, can be enclosed in a cylindrical vessel to separate both gases and liquids. The present invention is directed to a process of making and using improved microporous hollow fibers and tube bundles employing them.
2. Background of the Invention
U.S. Pat. No. 4,214,020 to Ward et al. discloses a coating for the exteriors of a plurality of hollow fibers which are suitable for fluid separation and which are assembled in the form of a bundle. The process includes the step of immersing the bundle of hollow fibers in a coating liquid containing material which is suitable for forming the coating. A pressure drop from the exterior to the interior of the hollow fibers results in the formation of a deposit on the exterior of the hollow fibers.
U.S. Pat. No. 4,806,246 to Nomura discloses a hydrophobic microporous membrane substrate which can be coated with a plasma polymerization coating. This coating reduces the pore size of the substrate to a size smaller than the original pore size but not less than 10 A. The plasma polymerization activates a monomer precursor into a high energy, dissociated form enriched with radicals, electrons, and ions and deposits a plasma polymer thereof onto the surface of the substrate moving through the glow zone. Nomura thus coats the exterior surface of the hollow fibers.
U.S. Pat. No. 3,874,899 to Miszenti et al. discloses the preparation of a semi-permeable membrane suitable for gas separations wherein a microporous layer of alumina is deposited on the inside of a sintered porous alumina tube by passing an aqueous suspension of the alumina through the inside of the tube and filtering the suspension through the walls of the tube.
U.S. Pat. No. 4,014,798 to Rembaum discloses the preparation of a porous hollow fiber which is impregnated with a polymer having quaternary amine sites. Rembaum discloses that the mixture of polymerized monomers extrudes through the pores of the walls and that excess particles blocking the central passage are removed by forcing liquid through the bore of the fiber.
U.S. Pat. No. 4,211,602 to Brumfield discloses blood dialyzers in which hollow fibers are potted in plastic tube sheets, and the tube sheets are then cut to form a manifold surface providing access to the interior of the hollow fibers.
Each of the foregoing are incorporated in their entirety by reference.
Polyperfluorosulfonic acid (PFSA) is an ion-exchange polymer which is available in flat sheet. PFSA is also available in solvent mixtures. PFSA sheet films are available from Dupont in thicknesses as low as 28 to 30 .mu.m.
Commercial ventures such as Perma-Pure manufacture and sell devices constructed of tubes of PFSA. These devices have wall thicknesses of approximately 130 to 150 .mu.m and outside diameters 1,680 .mu.m supported with an outside mesh of various materials.
PFSA is a very expensive polymer and thus it is desirable to use it in very thin thicknesses. However, none of the commercial suppliers have succeeded in manufacturing hollow fibers of the size typically used in hollow fiber membrane devices with outside diameters of about 240 .mu.m, wall thickness 30 .mu.m.
Fibers available as commercial products for hollow fiber membranes and devices include "CELGARD X-20" which is manufactured by Hoechst-Celanese. These fibers are available in commercial modules with several thousand fibers "potted" in a plastic shell equipped with the appropriate plumbing connections.
None of prior art provides a satisfactory solution to the problem of efficient gas to fluid separation. By means of the present invention, it is now plausible to assemble PFSA coated fibers into a tube bundle without destroying the coating. No one has previously attempted to coat the inside of an organic hollow fiber with PFSA. The high pressure side of separation is usually carried out on the inside of the fiber, and, thus, the exertion of pressure on the coated PFSA film is braced by the fiber wall in an expansion direction. Thus, the present invention avoids the risk of prior art coated fibers where the coating could be blown off. Conversely, if the high pressure is applied to the outside of a fiber coated on the outside as in the prior art in order to prevent the coating from being blown off, the hollow fiber could collapse. Thus, the present invention solves the foregoing problems and provides further advantages over the prior art as will become apparent from the following description.